Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 26, 2015	Sep. 26, 2015	Jun. 27, 2015	Mar. 28, 2015	Dec. 27, 2014	Sep. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Dec. 26, 2015	Dec. 27, 2014	Dec. 28, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income									$ 1,552	$ 2,287	$ 4,684
Provision for income taxes									(33,001)	(29,281)	(45,170)
Net income	$ 16,575	$ 12,788	$ 16,644	$ 13,323	$ 13,698	$ 13,511	$ 12,602	$ 14,570	59,330	54,381	73,186
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income									27	63	1,774
Provision for income taxes									(11)	(26)	(730)
Net income									$ 16	$ 37	$ 1,044